Moving equipment that uses insulative bearing arrangement, such as air bearing spindles, cannot be adequately grounded during operation since the bearing arrangement used are by definition insulative. In static-sensitive (electrostatic discharge—ESD) applications, such as disk drive and semiconductor equipment, it is important to assure a good ground connection between a rotor of the spindle and ground. In a typical system, a spring-loaded connection between rotor and ground is used. FIG. 1a depicts an example of a typical arrangement with a spindle 10 with its rotor 12 separated from the stator by an insulative bearing 14, such as an air bearing in this example. In this particular application, the air spindle drives a disk drive platter 16 during a test and a magnetic head 18 used for the test can be easily damaged if the voltage on the platter 16 is high which can be caused when the platter 16 (and the rotor 12) is not being grounded properly.
The grounding of the rotor is typically accomplished by a spring-loaded contact 20 physically and electrically connected to the stator, or frame, via arrangement 22. This contact is electrically connected typically to a special contact 20 at the center of the rotor wherein the arrangement 22 extends and connects to the spindle 10 by a screw 24. The special contact is usually called “button” and this document uses this definition for clarity. The special connection shown in FIG. 1a is not reliable since the button 20 wears off and also the spring of this contact can relax due to fatigue and therefore interrupt the contact as shown in FIG. 1b. When the contact is interrupted, the ground connection is lost and dangerous exposure of sensitive components to voltages and currents can occur. It is desirable to provide a device and method for being able to monitor the connection between the rotor and ground reliably and does not rely on the spring contact.
A conventional method of monitoring a ground connection by continuity (such as is shown in a Ground Master product commercially available from Credence Technologies, Inc. with further details of this product found at http://www.credencetech.com/products/product.php?productId=CTC065,%20CTC065RT) cannot be employed in this case since only one electrical contact of monitored part is available.
Thus, it is desirable to provide a device and method of monitoring ground connection of moving equipment with insulative bearing arrangement and it is to this end that the present invention is directed.